Heat-sensitive copying sheet



HEAT-SENSITIVE COPYING SHEET Filed Jan. 16, 1962 oARK C0./. 0R50 BackmeUnited States Patent O 3,164,484 HEAT-SENSITIVE CPYING SHEET Donald J.Lazzarini, North Bergen, NJ., assignor to Interchemical Corporation, NewYork, N.Y., a corporation of Ohio Filed Jan. 16, 1962, Ser. No. 166,6868 Claims. (Cl. 11T-36.7)

This invention relates to heat-sensitive copying paper useful inpreparing copies of printed matter or other graphic originals.

Heat-sensitive copying papers which operate by means of a physicalchange that is produced by heat are old in the art. U.S. Patent No.2,710,263 and Reissue Patent No. 24,554 described heat-sensitivecoatings for making copying paper in which the image appearing on thecopy sheet results from a physical change in the coating correspondingto the image copied. According to the teachings of these prior artpatents a heat-sensitive copying paper can be prepared by coating a darkcolored supporting base with a composition consisting of particles of anormally transparent stable organic fusible solid, melting within therange of 60-115 C., dispersed in a solution of a transparentfilm-forming binder in a volatile solvent, evaporating the solventwithout fusing or dissolving lthe particles so as to provi-de anon-transparent, infrared transmitting, heat-sensitive paper. Aprotective layer of film-forming material can be applied over theheat-sensitive layer if desired. Heating the sheet at temperaturescorresponding to the melting point of the fusible solid melts theheat-sensitive coating and allows the dark colored base sheet to showthrough at the heated areas. In making copies of graphic originals theheated areas would correspond to the image on the original and wouldresult from heat generated by exposing the original to high intensityinfrared radiation. Preferably the copy is made by placing the copysheet on the original with its uncoated side next to the original andthen exposing the original through the heat-sensitive copy sheet. In analternate technique, the original would be exposed to infrared radiationdirectly with the coated side of the heat-sensitive paper immediatelyback of it. By this back-printing technique it is not necessary, ofcourse, that the heat-sensitive paper be infrared transparent. Both theback-printing and the front-printing techniques are described in theprior art patents mentioned above and also in U.S. Patent No. 2,859,351.

A problem which has hampered the use of heat-sensitive coatings of thetype described in the afore-mentioned patents is that thepressure-sensitivity of such coatings is greater than is desirable; thatis the coatings are easily bruised and marred during handling, therebyallowing the dark colored base sheet to show through.

I have now made novel heat-sensitive copying sheets of greatlydiminished pressure sensitivity which comprise a non-metallic supportingbase preferably of a dark color having thereon a visibly opaqueheat-sensitive coating of a contrasting color. This coating comprises athin lm of a transparent film-forming organic binder having distributedtherein particles of a hydrated salt formed by the reaction of aninorganic hydroxide, preferably a metal hydroxide with either aninorganic acid or any carboxylic acid such as acetic acid which producesan inorganic type of salt. These inorganic types of salt are soluble ordecompose in hot (about 50 C.) water. In addition, the hydrated saltspreferably have a melting point between 60 and 120 C. Some operablesalts include hydrated aluminum sulfate, hydrated monobasic calciumphosphate and hydrated ferrous sulfate, as well as hydrated magnesiumacetate, hydrated sodium acetate and hydrated s` iurn potassiumtartrate.

3,164,484 Patented Jan. 5, 1.965

ICC

The novel heat-sensitive sheets of this invention are prepared byforming a dispersion of the hydratedV salt in a volatile organic solventin which a film-forming binder is dissolved. In addition to binder, thesolvent may also optionally contain plasticizer for the film to beformed.

The Volatile organic solvent may be any conventional volatile organicsolvent in which the selected hydrated salt is insoluble and in whichthe binder is soluble. The binder may be a polyacrylate such aspolymethylmethacrylate, a cellulosic polymer such as nitro-cellulose orethyl cellulose, a vinyl polymer such as polyvinyl chloride andpolyvinyl acetate.

Any plasticizer which is compatible with the binder may be optionallyused. Suitable plasticizers include, for example, n-butyl stearate,dibutyl phthalate, dibenzyl phthalate, tricresyl phosphate, tributoxyethyl phosphate, butyl phthalyl butyl glycollate, ethyl-o-benzoylbenzoate, dibenzyl sebacate and dioctyl sebacate.

Preferably from 3 to 7 parts by weight of hydrated salt are used foreach part of binder used and from 7 to 12 parts by weight of solvent areused for each part of binder used.

The base sheet may be any sheet conventionally used in makingheat-sensitive copying sheets which operate by means of physical change.The whole base sheet or at least the surface of said sheet which is tobe covered with the coating should be of a color contrasting with saidcoating, preferably a dark color.

Where the heat-sensitive sheets are to be employed in the production ofcopies of the front-printing technique, it is of course necessary thatboth the base sheet and coating be transparent to infrared light. Where,however, the back-printing technique is used, such infrared transparencyis not a necessity.

It is to be noted that unless otherwise stated all pro. portions in thespecification and claims are by weight.

The following examples will further illustrate the practice of theinvention.

Example 1 above C. and a molecular weight of 334,000 5.0 n-Butylstearate 3.0

are milled by suitable means such as a ball mill until theA12(SO4)3.18H2O has been formed into particles having a diameter in theorder of 0.5 to l mil and uniformly dispersed throughout the mixture.The composition is then coated uniformly on a black carbonizing tissueas a coating having a thickness of 0.5 mil. The coating can be appliedby conventional means, e.g., using a Mayer Rod coater. Upon drying agrayish-white opaque coating was produced. The resulting coated sheet ishighly mar land seuil-resistant and has a very low pressure sensitivity.The heat-sensitive sheet may be used to produce copies by the front orback printing techniques using the Thermo-Fax copying machine.

Example l is repeated. The heat-sensitive sheet produced has the sameproperties as that of Example 2 except that the pressure sensitivity ofthe sheet of this example is even llower than that of Example 1.

Example 3 Example l is repeated using the same ingredients, proportionsand conditions except that hydrated sodium ace-` tate, NaCgHSOZHZO, isused instead of hydrated aluminum sulfate. The heat-sensitive sheetproduced has the same properties as that of Example 1.

Example 4 Example 1 is repeated using the same ingredients, proportionsyand conditions except that hydrated `ferrous sulfate, FeSO4-7l-l20, isused instead of hydrated aluminum sulfate. The heat-sensitive sheetproduced has the same properties as that of Example l.

Example 5 Example 1 is repeated using the same ingredients, proportionsand conditions except that hydrated potassium sodium tartrate,NaKC4H4OS-4H2O, is used instead of hydrated aluminum sulfate. Theheat-sensitive sheet produced has the same properties as that of Example1.

Example 6 vention, it will be obvious to those skilled in the art thatvarious changes and modications may be made therein without departingfrom the invention, and it is, therefore, aimed to cover all suchchanges and modifications fas fall within the true spirit and Iscope ofthe in-v vention.

What is claimed is 1. A heat-sensitive copying sheet comprising anonmetallic supporting base and a visibly opaque heat-sensitive coatingof contrasting color thereon comprising a thin lm of a transparentfilm-forming organic binder having a dispersion therein consistingessentially of particles of a hydrated salt selected from the groupconsisting of hydrated aluminum sulfate, hydrated monobasic calciumphosphate, hydrated ferrous sulfate, hydrated magnesium acetate,hydrated sodium acetate and hydrated potassium sodium tartrate'from 3 to7 parts by weight of said hydrated `salt being present for each part ofthe binder.

2. The heat-sensitive copying sheet defined in claim 1, wherein saidparticles `are hydrated aluminum sulfate.

3. The heat-sensitive copying sheet dened in claim 1, wherein saidparticles are hydrated monobasic calcium phosphate.

4. The heat-sensitive copying sheet defined in claim 1, wherein saidparticles are hydrated ferrous sulfate.

5. The heat-sensitive copying sheet defined in claim 1, wherein saidparticles are hydrated magnesium acetate.

6. The heat-sensitive copying sheet delined in claim 1, wherein saidparticles are hydrated sodium acetate.

7. The heat-sensitive copying sheet defined in claim 1, wherein saidparticles are hydrated potassium sodium tartrate.

8. The heat-sensitive copying sheet dened in claim 1, wherein saidorganic binder comprises polymethylrnethacrylate.

References Cited in the file of this patent UNITED STATES PATENTS DaltonMar. 13, 1962

1. A HEAT-SENSITIVE COPYING SHEET COMPRISING A NONMETALLIC SUPPORTINGBASE AND A VISIBLY OPAQUE HEAT-SENSITIVE COATING OF CONTRASTING COLORTHEREON COMPRISING A THIN FILM OF A TRANSPARENT FILM-FORMING ORGANICBINDER HAVING A DISPERSION THEREIN CONSISTING ESSENTIALLY OF PARTICLESOF A HYDRATED SALT SELECTED FROM THE GROUP CONSISTING OF HYDRATEDALUMINUM SULFATE, HYDRATED MONOBASIC CALCIUM PHOSPHATE, HYDRATED FERROUSSULFATE, HYDRATED MAGNESIUM ACETATE, HYDRATED SODIUM ACETATE ANDHYDRATED POTASSIUM SODIUM TARTRATE FROM 3 TO 7 PARTS BY WEIGHT OF SAIDHYDRATED SAOT BEING PRESENT FOR EACH PART OF THE BINDER.